The present invention, in some embodiments thereof, relates to methods, kits and devices for promoting cardiac regeneration.
Heart regeneration is a primary biomedical research goal. Myocardial infarction (MI) is a life-threatening injury causing permanent loss of cardiomyocytes (CMs). MI events are experienced by over 900,000 people per year in the United States alone, and about one in four will die. Scars form in MI survivors, increasing susceptibility to compensatory pathology, aneurysm, additional MI events, heart failure, and sudden death. Thus, a major goal of regenerative medicine is to replenish lost CMs, avoid scar-associated pathology, and improve outcomes after MI. Adult mammalian cardiomyocytes (CMs) have limited proliferative capacity1, 2 with poor ability to replace lost tissue after acute ischemic injury3-7. Hence, a scientific and clinical imperative is to find ways of stimulating regenerative capacity in human hearts3-7. Cardiac and non-cardiac stem cell populations have been emphasized for use in heart regeneration therapies. However, there is general consensus that the modest benefits seen after stem cell transplantation do not arise from their differentiation into CMs1,2. Instead transplanted cells survive only transiently and likely affect endogenous repair mechanisms via paracrine action. The potential use of pluripotent stem cell-derived CMs for heart therapy also faces daunting challenges with cell maturation, arrhythmogenesis, immunosuppression, and the need for scale-up1,2. The ability to stimulate robust endogenous cardiac regeneration without adding exogenous cells would avoid these issues, and remains the field's “holy grail”.
Over the first week of postnatal life in mice, most CMs exit the cell cycle and continue to grow by hypertrophy (increase in cell size)8, 9, although they undergo an additional burst of proliferation in the pre-adolescent period10. Postnatal CM differentiation is paralleled in mice by bi-nucleation of CMs and in humans by increased ploidy8, 9. The molecular mechanisms regulating the transition from CM hyperplastic (increase in cell number) to hypertrophic growth at early postnatal stages, and in particular how CM proliferation capacity might be re-activated in adult life to foster regeneration, are poorly understood.
A robust regenerative response to injury occurs in adult hearts of lower vertebrates such as zebrafish and amphibians4, 11. Regeneration has also been demonstrated in mammalian hearts during the first week of postnatal life12, corresponding to the time window during which CMs continue to proliferate9, and by post-natal day 7 (P7) fibrotic scar formation predominates over tissue replacement12. In adult zebrafish and neonatal mice, the regenerative response involves CM proliferation4, 11-13.
Signalling networks that drive embryonic heart development may also control aspects of heart regeneration6, 14. The ligand-receptor network consisting of Neuregulin-1 (NRG1), and its tyrosine kinase receptors ErbB4, ErbB3 and ErbB2, plays critical roles during heart development15-20. ErbB4 and ErbB2 are the NRG1 receptors expressed most prominently in embryonic, fetal and neonatal CMs, and recombinant NRG1 stimulates embryonic/fetal/neonatal CM proliferation, hypertrophic growth, sarcomerogenesis and survival ex vivo18, 21. Decreased NRG1 signalling in postnatal hearts is associated with adverse cardiac function and susceptibility to stress22, 23. Administration of NRG1 improves cardiac function following injury in adult mice22-27 and in heart failure patients22, 23.25, 28-31. However, recent advanced clinical trials did not reach the expected results, suggesting a missing component in the Nrg-1 signalling pathway. This was suggested to stem from multiple mechanisms, including improved CM survival and contractility22 as well as induction of adult CM proliferation26, although the contribution of the latter one is controversial22, 32. Nevertheless, how ErbB2 impacts cardiac regeneration is unknown.
The Erbb2 gene was originally identified due to its oncogenic activity and its overexpression is associated with poor prognosis in cancer patients33-35. Unlike ErbB4, ErbB2 is unable to bind ligands, yet, it is the preferred hetero-dimerization partner, stabilizing ligand binding, enhancing and diversifying ligand-induced receptor signalling34, 36-38. In the myocardium, ErbB2 forms heterodimers with ErbB439.